1. Technical Field
The present invention relates in general to an improved disk drive, and in particular to an improved system and method for enhancing the loading and unloading performance of low-flying heads in a disk drive.
2. Description of the Prior Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, two or three disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
A typical HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with an aerodynamic pattern of protrusions (air bearing design) on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each platter and flies just over the platter""s surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop directly over the desired track.
One problem associated with load/unload disk drives is the risk of undesirable slider/disk contacts during the load operation due to the relatively large distances that the head must move to initiate a read/write operation. Such a contact can damage the head and/or the disk, thereby reducing the performance of or completely disabling the drive. A number of solutions have been proposed to reduce this risk, such as those of U.S. Pat. Nos. 6,057,984, and 5,303,099. These approaches teach one to spin the disks up to higher speeds to increase the flying height, and to control the flying height over the bumps, respectively. However, in both cases, the flying height is being adjusted within the normal flying height range of 10 to 20 nm, or much less than 100 nm are more applicable to contact-start-stop drives. Although these designs are workable, the heads are still vulnerable to contacting the disk since the slider comes very close to the disk surface during a loading operation. An improved solution is needed.
In one embodiment of a disk drive constructed in accordance with the present invention, the slider is designed to fly very high or well above the surface of the disk when loading onto the disk and until a reading or writing operation requires the head to go into pseudo-contact or a relatively low-flying position with respect to the disk. Thus, the slider has two or more altitudes at which it flies depending on the operating conditions of the disk drive. The different altitudes of the slider are achieved by adjusting three primary variables: the rotational speed of the disk, selecting the radial position of the slider/actuator arm, and gram load. Other factors that may be used to tune this performance include pitch static attitude, pitch stiffness, and air bearing surface design.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.